The Activ 4 square back chair comes with a plastic outer shell and medium sized seat. The Activ Posture range of chairs have the option to include the unique air-care technology system, providing superior enhanced comfort in the seat. The technology provides

Pressure sensitive relief to the coccyx area
Encourages correct posture.
Offers superior weight distribution
Encourages active sitting
Aids in reduction of spinal compression and improves core stability
This chair is designed to follow your movements. With a free floating mechanism the chair pivots at the centre of the seat, allowing an infinite lock if required.

The key to this mechanism is that the backrest and seat move together, maintaining the open pelvic angle and keeping the lumbar support in the position that you need it.